Interferometric systems are suitable for, among other things, contactless examinations of surfaces of different measured objects. To register the surface contour of an object to be examined, an object beam from a light source of the interferometer is incident on the surface of the region to be measured. The object beam reflected from the surface is fed to a detector of the interferometer and produces, together with a reference beam, an interference pattern from which the optical path length difference of the two beams may be derived. This measured optical path length difference of the two beams corresponds to the topography change of the surface.
In particular using a white-light interferometer, in which the light source emits short coherent radiation, it is also possible to scan the measured object using depth scanning. As explained in German Patent Application No. DE 103 25 443.9 (not a prior publication), for example, the short coherent radiation is divided via a beam splitter into an object beam and a reference beam. The object surface to be measured is imaged via an objective on an image recorder, such as a CCD camera (“charge-coupled device” camera) and has the reference wave produced by the reference beam superimposed thereon. Depth scanning may be performed by moving a reference mirror which reflects the reference beam or the objective in relation to the measuring device. As the object moves, the image plane of the object and the reference plane are in the same plane. During depth scanning, the object remains fixed in the visual field of the CCD camera, and the object is only moved in the depth axis in relation to the reference plane. In this way, technical surfaces may be measured with a depth resolution in the range of a few nanometers. The technical foundations of this measurement method are also found in the article “Three-dimensional sensing of rough surfaces by coherence radar” (T. Dresel, G. Häusler, H. Venzke, Appl. Opt. 31 (7), pp. 919-925, 1992).
If the surface of the object to be measured in this case is not a uniform, flat plane, a special objective is necessary for measuring the object. This is because it must be ensured during every measurement procedure that the beams are incident perpendicularly on the surfaces to be measured during scanning. For example, a system of optical elements, using which even conical surfaces may be measured, is described in German Patent Application No. DE 101 31 778. Using the panoramic lens presented therein, even surfaces whose shape corresponds to the inner or outer surfaces of a cone may be measured. The beams are deflected by the panoramic lens onto the different surfaces of the measured object, which are not parallel to one another, in such a way that they are incident perpendicularly on the particular measured surfaces. However, no splitting of the beams incident on the panoramic lens into measurement and reference beams is provided. Therefore, a relative comparison of the conical measured surfaces of the measured object to preferably planar reference surfaces is not possible.